Printed circuit board

ABSTRACT

A printed circuit board includes a base formed from a plurality of woven fibers, and signal traces laid on the base. Each of the signal traces includes at least a straight line segment. The signal traces are laid on the base in such a manner that the line segments of the signal traces mapped on the base cross the fibers at angles not equal to zero degrees.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed circuit board, and moreparticularly to a printed circuit board having high signal transmissionquality.

2. Description of Related Art

Printed circuit boards (PCBs) typically consist of three principalcomponents: a base, resin, and copper foil. The base for a PCB is oftenconstructed from woven glass fiber cloth. In the process formanufacturing the PCB, the base is treated by passing it through a dippan containing resin. The treated base is then passed through a set ofsqueeze rollers, and then a drying oven to cure. Then, the base is cutinto a sized base which has a size of the PCB. Once the base has beenprepared, copper foil is applied to one or two sides of the base,typically by electrodeposition. The copper foil is etched to formdifferent signal traces on the PCB.

Referring to FIGS. 1 and 2, a PCB 1 includes a base 10 which includes aset of first fibers 11 and a set of second fibers 12. The PCB 1 definesan X-axis extending in a horizontal direction, and a Y-axisperpendicular to the X-axis. The set of first fibers 11 of the base 10disposed in the X-axis direction are interlaced with the set of secondfibers 12 of the base 10 disposed in the Y-axis direction. Resin isimpregnated in gaps 13 among the fibers 11 and 12. Generally, eachstraight line segment of a signal trace 17 is arranged on the PCB 1 atan angle of 0, 45, 90, −45 degrees relative to the X-axis. In a PCB,some line segments of the signal traces 17 will cross the fibers 11 or12 of the base 10 (such as the line segment of the signal traces 17arranged at the angles of 45, −45 degrees of FIG. 1), and some linesegments of signal traces will be coincident with the fibers 11 or 12 ofbase 10 (such as the line segment of signal traces arranged at theangles of 0, 90 degrees of FIG. 1). Because the fibers 11, 12 and theresin have different dielectric constants, impedances of differentsignal traces 17 vary over a large range according to the locations andthe angles of the line segments of the signal traces 17 relative to thebase 10. However, in a PCB, if the impedances of different signal tracesvary greatly, the delay times of signals on different signal traces willbe very different.

SUMMARY OF THE INVENTION

A printed circuit board includes a base formed from a plurality of wovenfibers, and signal traces laid on the base. Each of the signal tracesincludes at least a straight line segment. The signal traces are laid onthe base in such a manner that the line segments of the signal tracesmapped on the base cross the fibers at angles not equal to zero degrees.

Other advantages and novel features of the present invention will becomemore apparent from the following detailed description of preferredembodiment when taken in conjunction with the accompanying drawings, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a conventional PCB including a first kindof base and a plurality of signal traces;

FIG. 2 is a cross sectional view taken along line II-II in FIG. 1;

FIG. 3 is an enlarged view of an encircled portion III of FIG. 1;

FIG. 4 is a schematic view of a PCB in accordance with a preferredembodiment of the present invention applied on the first kind of base ofFIG. 1;

FIG. 5 is a schematic view of another PCB in accordance with a preferredembodiment of the present invention applied on a second kind of base;

FIG. 6 is a schematic view of another PCB in accordance with anotherpreferred embodiment of the present invention applied on the second kindof base of FIG. 5;

FIG. 7 is a schematic view of a first manner to produce the PCB of thepresent invention; and

FIG. 8 is a schematic view of a second manner to produce the PCB of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 3, an enlarged encircled portion III of the base 10 ofFIG. 1 is shown. Two adjacent parallel first fibers 11 and two adjacentparallel second fibers 12 perpendicular to the fibers 11, togetherdefine a square area 15 (shown with dashed lines in FIG. 3) that is Llong along the fibers 11 and W wide along the fibers 12, whereinL=17.86×10⁻³ inches, and W=17.86×10⁻³ inches. An angle φ between thefirst fiber 11 and a diagonal of the area 15 is 45 degrees. An angle θbetween the second fiber 12 and the diagonal of the area 15 is also 45degrees.

Referring to FIG. 4, when the signal traces 17 of the PCB 1 in FIG. 1 isrotated an angle α which is equal to half of one of the angles φ, θ andis 22.5 degrees in this embodiment relative to the Y-axis in acounter-clockwise direction on the PCB 1 with other elements on the PCB1 remaining unchanged we achieve PCB 1′ of a first embodiment of thepresent invention. On the PCB 1′, any line segment of the signal traces17 is not coincident with the fibers 11, 12 and the diagonals of theareas 15 of base 10. The angle between any line segment of the signaltraces 17 and any fiber 11 or 12 is not smaller than 22.5 degrees. Sothe impedances of the signal traces 17 are kept in a small range toimprove signal transmission quality.

It is to be understood that in the above embodiment the signal traces 17also can be rotated in a clockwise direction, or rotates the base 10relative to the signal traces 17. Furthermore, the value of the rotatedangle α is not limited to half of the angles φ, θ. Any angle can be usedin the present invention as long as any line segments of the signaltraces 17 are not coincident with the fibers 11, 12 and the diagonals ofthe areas 15 of base 10 after rotation.

Referring to FIG. 5, a second kind of base 30 is placed on a plane 5.The plane 5 defines an X-axis extending in a horizontal direction, and aY-axis perpendicular to the X-axis. The base 30 includes a set of firstfibers 31 and a set of second fibers 32. The set of first fibers 31 ofthe base 30 disposed in the X-axis direction are interlaced with the setof second fibers 32 of the base 30 disposed in the Y-axis direction. Twoadjacent parallel first fibers 31 and two adjacent parallel secondfibers 32 perpendicular to the fibers 31, together define a rectangulararea 35 (shown with dashed lines in FIG. 5) that is L′ long and W′ wide,wherein L′=21.28×10⁻³ inches, and W′=17.86×10⁻³ inches. An angle φ′between the first fiber 31 and a diagonal of the area 35 is arc tanL′/W′=52 degrees. An angle θ′ between the second fiber 32 and thediagonal of the area 35 is arc tan W′/L′=38 degrees. When therectangular area 35 is not square-shaped, an angle α′ being equal tohalf of the smaller one of the angles φ′, θ′ is set, in the secondembodiment angle α′=19 degrees.

In normal manner for laying signal traces on the base 30, signal tracesare laid on the base 31 to have one of the straight line segments of thesignal traces been coincident with the X-axis of the base 30, forexample, the straight line segments of the signal traces arranged on thebase 30 at an angle of 0, 45, 90, −45 degrees relative to the X-axis ofthe base 30. However, to achieve the second embodiment of the presentinvention, each signal trace 37 laid on the base 31 in an abnormalmanner is rotated 19 degrees relative to the original position of eachsignal trace 37 laid in the normal manner. Thus, the straight linesegments of the signal traces 37 are arranged on the base 30 at an angleof 19, 64, 109, −26 degrees relative to the X-axis of the base 30. Sothe line segments of the signal traces 37 are not coincident with thefibers 31, 32 and the diagonals of the areas 35 of the base 30. Theimpedances of the signal traces 37 are kept in a small range therebyproviding quality signal transmission.

Referring to FIG. 6, a set of parallel signal traces 47 are laid on thebase 30. The parallel signal traces 47 are laid in the abnormal manneras described above. Any line segment of the signal traces 47 is notcoincident with the fibers 31, 32 and the diagonals of the areas 35 ofthe base 30. The impedances of the set of signal traces 47 aresubstantially uniform, and the delay times of signals on the set ofparallel signal traces 47 will be uniform.

To achieve the PCBs in the above embodiment, there are several differentmanners. FIG. 7 shows a kind of manner. A large base 70 is preparedfirstly. The base 70 is constructed from the same glass fiber cloth asthe base 30 of FIG. 5. The base 70 also defines the X-axis along whichthe parallel first fibers extend, and the Y-axis perpendicular to theX-axis. The parallel second fibers extend along the Y-axis. The base 70is then cut into four rectangular uniform sized bases 71, which have thesame size of the final PCB, in a normal manner which means two paralleledges of the sized bases 71 are parallel to the first fibers and theother two parallel edges of the sized bases 71 are parallel to thesecond fibers. In normal manner for laying signal traces, signal tracesare laid on the sized base 71 to have one of the straight line segmentsof the signal traces been coincident with the X′-axis of the base 70,for example, the straight line segments of the signal traces arranged onthe sized base 71 at an angle of 0, 45, 90, −45 degrees relative to theX-axis of the base 70. However, to achieve the embodiments of thepresent invention, each signal trace 73 is laid on the sized base 71 inan abnormal manner and is rotated an angle relative to the originalposition of each signal trace laid in the normal manner. In the base 70,the rotated angle is 19 degrees as that in the base 30 of FIG. 5. Thus,the straight line segments of the signal traces 73 are arranged on thesized base 71 at an angle of 19, 64, 109, −26 degrees relative to theX′-axis of the base 70. So substantially all line segments ofsubstantially all signal traces 73 mapped on the base cross the fibersof the base 70 at angles not equal to zero degrees.

FIG. 8 shows another kind of manner to product the PCBs. The base 70 iscut into four rectangular sized bases 81 in an abnormal manner to havetwo parallel edges of each sized base 80 crossing the X-axis directionof the base 81 with an oblique angle. The oblique angle is 19 degrees.The sized base 81 defines an X′-axis angled relative to the X-axis with19 degrees. Signal traces 83 are laid on the sized base 81 in the normalmanner which means one of the straight line segments of the signaltraces being coincident with the X″-axis of the sized base 80, forexample, the straight line segments of the signal traces 81 beingarranged on the sized base 81 at angles of 0, 45, 90, or −45 degreesrelative to the X″-axis of the sized base 81. So substantially all linesegments of substantially all signal traces 83 mapped on the base crossthe fibers of the base 70 at angles not equal to zero degrees.

After the invention was made, applicants tested the invention to measurethe signal delay times of different signal traces, and compare the datawith measured delay times of a conventional PCB. A conventional PCB,using the base 30 of FIG. 5 without rotation, was found to have delaytimes of 152.8×10^('112) seconds per inch when signals were transmittedthrough signal traces having line segments coincident with the fibers 31or 32. If line segments of the signal traces crossed over the fibers 31or 32 of the base 30 at an angle, the delay times were found to be148.6×10⁻¹² seconds per inch, a difference between two delay times of4.2×10⁻¹² seconds per inch. On the PCB of the present invention (rotatedas in FIG. 6) however, signal traces with line segments extending 0 or90 degrees relative to the X′ axis, had delay times of 150.3×10⁻¹²seconds per inch, and signal traces with line segments extending 45 or−45 degrees relative to the X′ axis, had delay times of 150.4×10⁻¹²seconds per inch, a difference of only 0.1×10⁻¹² seconds per inch. Fromthe above data, it is apparent that signal transmission quality isimproved when using the present invention.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size, and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

1. A printed circuit board, comprising: a base formed from a pluralityof woven fibers; and signal traces laid on the base, each of the signaltraces comprising at least a straight line segment, the signal traceslaid on the base in such a manner that the line segments of the signaltraces mapped on the base cross the fibers at angles not equal to zerodegrees.
 2. The printed circuit board as described in claim 1, whereinthe fibers comprise a set of parallel first fibers, and a set ofparallel second fibers perpendicular to and interlaced with the set offirst fibers.
 3. The printed circuit board as described in claim 2,wherein two adjacent first fibers and two adjacent second fibers definea rectangular area thereamong, the line segments of the signal tracesmapped on the base cross diagonals of the rectangular area at angles notequal to zero degrees.
 4. The printed circuit board as described inclaim 3, wherein a first angle is defined by the first fiber and thediagonal of the rectangular area, and a second angle is defined by thesecond fiber and the diagonal of the rectangular area, the angle definedby each line segment of each signal trace and each corresponding fiberthe line segment crosses is not smaller than half of the smaller one ofthe first and second angles.
 5. The printed circuit board as describedin claim 3, wherein a first angle is defined by the first fiber and thediagonal of the rectangular area, and a second angle is defined by thesecond fiber and the diagonal of the rectangular area, the angle definedby each straight line segment of each signal trace and one correspondingfiber it cross is equal to half of the smaller one of the first andsecond angles.
 6. The printed circuit board as described in claim 5,wherein the printed circuit board defines an X-axis along which theparallel first fibers extend, and a Y-axis perpendicular to the X-axis,and the straight line segments of the signal traces are arranged on theprinted circuit board in a direction at an angle of α, 45+α, 90+α, orα−45 degrees relative to the X-axis of the printed circuit board, α isequal to half of the smaller one of the first and second angles.
 7. Aprinted circuit board, comprising: a base formed from a plurality ofwoven fibers, the fibers comprising a set of parallel first fibers and aset of parallel second fibers perpendicular to and interlaced with theset of first fibers, two adjacent first fibers and two adjacent secondfibers defining a rectangular area thereamong, a first angle defined bythe first fiber and the diagonal of the rectangular area, and a secondangle defined by the second fiber and the diagonal of the rectangulararea; and a set of parallel signal traces laid on the base, each of thesignal traces comprising at least a straight line segment, the straightline segments of the parallel signal traces being designed to cross thefirst fibers at angles larger than zero and smaller than the first angleor cross the second fibers at angles larger than zero and smaller thanthe second angle.
 8. The printed circuit board as described in claim 7,wherein the angle defined by each line segment of each signal trace andone corresponding fiber the line segment cross is not smaller than halfof the smaller one of the first and second angles.
 9. The printedcircuit board as described in claim 7, wherein the angle defined by eachline segment of each signal trace and each corresponding fiber it crossis equal to half of the smaller one of the first and second angles. 10.The printed circuit board as described in claim 7, wherein the printedcircuit board defines an X-axis extending in a horizontal direction, anda Y-axis perpendicular to the X-axis, and each line segment of thesignal traces is arranged on the printed circuit board at an angle of α,α+45, α+90, or α−45 degrees relative to the X-axis of the printedcircuit board, α is equal to half of the smaller one of the first andsecond angles.
 11. A method for producing a printed circuit board,comprising the steps of: providing a large base, the base defining anX-axis and a Y-axis perpendicular to the X-axis, the base formed of aset of parallel first fibers extending in the X-axis direction and a setof parallel second fibers extending in the Y-axis direction, the firstfibers and the second fibers interlaced with each other; cutting thebase into a sized base which has a size of the printed circuit board;and laying signal traces each having at least one straight line segmenton the sized base in such a manner that the line segments of the signaltraces mapped on the base cross the fibers of the base at angles notequal to zero degree.
 12. The method as described in claim 11, whereinthe sized base has a rectangular configuration, the base is cut in anabnormal manner such that two parallel edges of the sized base cross theX-axis direction of the base with an oblique angle, and the signaltraces are laid on the sized base in a normal manner such that at leastone of the straight line segments of the signal traces is coincidentwith the parallel edges of the sized base.
 13. The method as describedin claim 12, wherein two adjacent first fibers and two adjacent secondfibers define a rectangular area thereamong, a first angle is defined bythe first fiber and the diagonal of the rectangular area, and a secondangle is defined by the second fiber and the diagonal of the rectangulararea, the oblique angle is equal to half of the smaller one of the firstand second angles.
 14. The method as described in claim 12, wherein thesized base defines an X′-axis crossing the X-axis with the obliqueangle, and the signal traces are laid such that the straight linesegments of the signal traces are arranged on the sized base at anglesof 0, 45, 90, or −45 degrees relative to the X′-axis of the sized base.15. The method as described in claim 11, wherein the sized base has arectangular configuration, the base is cut in a normal manner such thattwo parallel edges of the sized bases are parallel to the first fibersand the other two parallel edges of the sized bases are parallel to thesecond fibers, and the signal traces are laid in an abnormal manner suchthat the line segments of the signal traces mapped on the base cross thefibers of the sized base at angles not equal to zero degrees.
 16. Aprinted circuit board, comprising: a base comprising a plurality ofparallel first fibers and parallel second fibers perpendicular to andinterlaced with the first fibers, two adjacent first fibers and twoadjacent second fibers defining a rectangular area thereamong; andsignal traces each comprising at least a straight line segment, thesignal traces being laid on the base in such a manner that the straightline segments of the signal traces are not coincident with the fibers orthe diagonals of the rectangular areas when mapped on the base.
 17. Theprinted circuit board as claimed in claim 16, wherein the printedcircuit board defines an X-axis along which the parallel first fibersextend and a Y-axis along which the parallel second fibers extend, afirst angle is defined by the first fiber and the diagonal of therectangular area and a second angle is defined by the second fiber andthe diagonal of the rectangular area, and the straight line segments ofthe signal traces are crossed at one point and arranged on the base withangles of α, 45+α, 90+α, or α−45 degrees relative to the X-axis, α beingequal to half of the smaller one of the first and second angles.
 18. Theprinted circuit board as claimed in claim 16, wherein the printedcircuit board defines an X-axis along which the first fibers extend anda Y-axis along which the second fibers extend, a first angle is definedby the first fiber and the diagonal of the rectangular area and a secondangle is defined by the second fiber and the diagonal of the rectangulararea, and the straight line segments of the signal traces are parallelto each other and arranged on the base with angles of α degrees relativeto the X-axis, α being equal to half of the smaller one of the first andsecond angles.